It is now recognized that tumor regression and prognosis in neuroblastoma are closely associated with the stage of the malignancy at time of diagnosis. Evidence for in vitro lymphocyte cytotoxicity, blocking and unblocking factors, has been recognized in this neoplasm. The exact effect of various forms of conventional treatment on in vitro lymphocyte tumor immunity and general immuno-competence in this malignancy is not known. The purpose of this investigation is to study and evaluate the role of lymphocyte microcytotoxicity and of blocking and unblocking factors in patients with various stages of neuroblastoma at the time of diagnosis in order to determine if any specific correlative pattern exists and to study these immune parameters before, during and after therapy and during clinical remission and relapse to determine what changes occur under these circumstances. These studies will be performed by obtaining tumor tissue and normal tissue from patients with neuroblastoma and other tumors at the time of surgery. Tissue culture cell lines will be established from these tissues, and multiple aliquots of tumor cells and normal cells will also be frozen for later culturing and testing. Peripheral blood lymphocytes and sera will be obtained at the time of diagnosis of patients with neuroblastoma and tests for lymphocyte microcytotoxicity, blocking and unblocking factors will be performed, initially with allogeneic tumor and normal cultured cell lines and subsequently with both autochthonous and allogeneic cultured cell lines. At these same intervals, lymphocyte blastogenesis will be determined in cultures using phytohemagglutinin (PHA), allogeneic leukocytes and antigens as stimulants. Results of this study may provide important information concerning the role of cell and humoral mediated immunity in the host response to neuroblastoma.